Nano generator and method of manufacturing the same

ABSTRACT

A nanogenerator with at least one nanostructure and method of manufacturing the same are provided. The method of manufacturing the nanogenerator includes forming at least one nanostructure including an organic piezoelectric material on a substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2011-0079717, filed on Aug. 10, 2011 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

The present disclosure relates to nanogenerators and methods ofmanufacturing the same, and more particularly, to a nanogenerator with ananostructure including an organic piezoelectric material and a methodof manufacturing the same.

2. Description of the Related Art

Recently, much attention has been paid to energy harvestingtechnologies. Among energy harvesting devices, an energy generator usingpiezoelectric characteristics is a new type of environment-friendlyenergy generator. An energy generator converts mechanical energy,generated, e.g., from fine vibrations or the motion of a human body inan ordinary living environment, into electrical energy, unlikegenerators such as solar cells, wind power generators, and fuel cells.Furthermore, with recent advances in nano technology, it is possible toeasily manufacture nano-sized devices. However, the batteries that aregenerally used as power supply sources for the nano-sized devices arenot only far bulkier than the nano devices, but they also have a limitedlifetime. Accordingly, the use of batteries may degrade the performanceof a nano device and prevent the nano device from being independentlydriven.

To solve such problems, nanogenerators that use a nano-sizedpiezoelectric material have been developed. However, in general,nanogenerators using piezoelectric characteristics are manufacturedusing a zinc oxide (ZnO) piezoelectric material, and thus they have lowenergy efficiency.

SUMMARY

According to an aspect of an embodiment, there is provided ananogenerator including at least one nanostructure including an organicpiezoelectric material.

The organic piezoelectric material may be a ferroelectric material.

The organic piezoelectric material may be polyvinylidene fluoride(PVDF).

The nanogenerator may further include a substrate, and a first electrodedisposed apart from the substrate. The least one nanostructure may bedisposed between the substrate and the first electrode.

The substrate may include a conductive material.

The nanogenerator may further include a second electrode on thesubstrate.

The at least one nanostructure may be disposed perpendicularly orinclined at a predetermined angle with respect to the substrate.

A stack structure of the at least one nanostructure and a thirdelectrode on the at least one nanostructure may be formed at least onceon the first electrode.

The nanogenerator may further include a plurality of electrodes disposedapart from one another, and the least one nanostructure may be disposedbetween the plurality of electrodes.

The plurality of electrodes and the at least one nanostructure may bedisposed on the substrate.

The plurality of electrodes may be disposed in parallel at predeterminedintervals.

The at least one nanostructure may be disposed perpendicularly orinclined at a predetermined angle with respect to the plurality ofelectrodes.

The plurality of electrodes may be connected in series.

According to an aspect of another embodiment, a method of manufacturinga nanogenerator includes forming at least one nanostructure including anorganic piezoelectric material on a substrate.

The organic piezoelectric material may be PVDF.

The method may further include forming a first electrode on the at leastone nanostructure.

The method may further include forming a second electrode on thesubstrate.

The at least one nanostructure may be formed to be perpendicular orinclined at a predetermined angle with respect to the substrate.

The method may further include forming a stack structure of the at leastone nanostructure and a third electrode on the at least onenanostructure, on the first electrode, at least once.

The method may further include forming a plurality of electrodes on thesubstrate to be parallel with one another at predetermined intervals.

The at least one nanostructure may be formed between the plurality ofelectrodes.

The forming of the at least one nanostructure may include forming ananodic metal oxide template including a metal layer and a porous layeron the metal layer; filling the porous layer with a solution containingthe organic piezoelectric material; forming the at least onenanostructure by poling the organic piezoelectric material; and removingthe anodic metal oxide template.

The solution is filled in the porous layer when a temperature of thesolution is at about 50° C. to about 250° C.

The organic piezoelectric material may be poled when a temperature ofthe organic piezoelectric material is at about 50° C. to about 250° C.

The method may further include removing a thin film on the porous layerby using the solution.

The forming of the at least one nanostructure may include forming ananodic metal oxide template including a metal layer and a porous layeron the metal layer; removing the metal layer from the anodic metal oxidetemplate; filling the porous layer with a solution containing theorganic piezoelectric material; forming the at least one nanostructureby poling the organic piezoelectric material; and removing the porouslayer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings of which:

FIG. 1A is a schematic perspective view of a nanogenerator according toan embodiment;

FIG. 1B is a schematic front sectional view of the nanogenerator of FIG.1A;

FIG. 2A is a schematic perspective view of a nanogenerator according toanother embodiment;

FIG. 2B is a schematic top plan view of the nanogenerator of FIG. 2A;

FIGS. 3A to 3C are schematic cross-sectional views sequentiallyillustrating a method of manufacturing a nanogenerator, according to anembodiment;

FIGS. 4A to 4D are schematic cross-sectional views sequentiallyillustrating a method of manufacturing a nanostructure included in ananogenerator, according to an embodiment;

FIGS. 5A to 5E are schematic cross-sectional views sequentiallyillustrating a method of manufacturing a nanostructure included in ananogenerator, according to another embodiment;

FIGS. 6A and 6B are schematic cross-sectional views sequentiallyillustrating a method of manufacturing a nanogenerator, according toanother embodiment; and

FIG. 7 is a schematic cross-sectional view of a nanogenerator accordingto another embodiment.

DETAILED DESCRIPTION

Various exemplary embodiments will now be described more fully withreference to the accompanying drawings in which some exemplaryembodiments are shown.

Detailed illustrative exemplary embodiments are disclosed herein.However, the specific structural and functional details disclosed hereinare merely representative, and the present disclosure should not beconstrued as limited to only the exemplary embodiments set forth herein.

Accordingly, while example embodiments are capable of variousmodifications and alternative forms, embodiments thereof are shown byway of example in the drawings and will herein be described in detail.It should be understood, however, that there is no intent to limitexemplary embodiments to the particular forms disclosed, but on thecontrary, example embodiments are to cover all modifications,equivalents, and alternatives falling within the scope of the invention.Like numbers refer to like elements throughout the description of thefigures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the exemplary embodiments.As used herein, the term “and/or,” includes any and all combinations ofone or more of the listed items.

It will be understood that when an element or layer is referred toherein as being “formed on,” another element or layer, it may bedirectly or indirectly formed on the other element or layer. Forexample, intervening elements or layers may be present. In contrast,when an element or layer is referred to herein as being “directly formedon,” to another element, there are no intervening elements or layerspresent. Other words used to describe the relationship between elementsor layers are to be interpreted in a like fashion (e.g., “between,”versus “directly between,” “adjacent,” versus “directly adjacent,”etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exemplaryembodiments. As used herein, the singular forms “a,” “an,” and “the,”are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “comprises,” “comprising,” “includes,” and/or “including,” whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

In the drawings, the thicknesses of layers and regions may beexaggerated for clarity. Like reference numerals in the drawings denotelike elements.

Hereinafter, nanogenerators and methods of manufacturing the sameaccording to various embodiments will be described in detail withreference to the accompanying drawings.

FIG. 1A is a schematic perspective view of a nanogenerator 100 accordingto an embodiment. FIG. 1B is a schematic front sectional view of thenanogenerator 100 of FIG. 1A.

Referring to FIGS. 1A and 1B, the nanogenerator 100 may include asubstrate 110, a first electrode 130 disposed apart from the substrate110 by a predetermined distance, and at least one nanostructure 140disposed between the substrate 110 and the first electrode 130. Thenanogenerator 100 may further include a second electrode 120 disposed onthe substrate 110. The at least one nanostructure 140 may be disposedbetween the first and second electrodes 130 and 120.

Any of various types of substrates may be used as the substrate 110. Forexample, the substrate 110 may be a solid substrate, such as a glasssubstrate or a silicon substrate, or a flexible substrate, such as aplastic substrate or a textile substrate, but aspects of the presentinvention are not limited thereto.

The first electrode 130 may be disposed apart from the substrate 110 bya predetermined distance, and the second electrode 120 may be furtherdisposed on the substrate 110. Each of the first electrode 130 and thesecond electrode 120 may be formed of a material selected from the groupconsisting of gold (Au), silver (Ag), aluminum (Al), copper (Cu),palladium (Pd), platinum (Pt), ruthenium (Ru), or mixtures thereof. Inother embodiments, each of the first electrode 130 and the secondelectrode 120 may be formed of an indium tin oxide (ITO), a carbonnanotube, a conductive polymer, nanofiber, a nanocomposite, or graphene.However, the materials of the electrodes are not limited thereto. Whenthe substrate 110 contains a conductive material, the substrate 110 maybe used as an electrode instead of the second electrode 120. Forexample, if the substrate 110 contains high-concentration doped silicon,the second electrode 120 may not be formed on the substrate 110.

At least one nanostructure 140 may be disposed between the firstelectrode 130 and the second electrode 120. The at least onenanostructure 140 may be formed on the second electrode 120 in an m×n 2Darray. Here, m and n each denote a natural number. In other words, onenanostructure 140 may be disposed on the second electrode 120 or aplurality of nanostructures 140 may be disposed in parallel on thesecond electrode 120 to be apart from one another by a predetermineddistance. Also, the at least one nanostructure 140 may be disposedperpendicularly or inclined at a predetermined angle with respect to thesubstrate 110.

The at least one nanostructure 140 may include an organic piezoelectricmaterial, e.g., a ferroelectric material. For example, the at least onenanostructure 140 may include polyvinylidene fluoride (PVDF). Morespecifically, the at least one nanostructure 140 may include β-phasePVDF. If the at least one nanostructure 140 includes PVDF, the at leastone nanostructure 140 may be formed using an anodic aluminum oxidetemplate. The at least one nanostructure 140 may include a nanorod, ananowire, or a nanotube. The nanorod and the nanowire may have differentaspect ratios. For example, the aspect ratio of the nanowire may begreater or less than that of the nanorod. The size and sectional shapeof the at least one nanostructure 140 may vary according to those of theanodic aluminum oxide template.

An external load 150 may be connected to the first and second electrodes130 and 120 to store electricity generated by the nanogenerator 100 orto consume the electricity. For example, if the external load 150 is acapacitor, the electricity generated by the nanogenerator 100 may bestored in the capacitor. If the external load 150 is a nano device, theelectricity generated by the nanogenerator 100 may be consumed by thenano device.

A mechanical force, e.g., fine vibrations, wind, sound, or a motion of ahuman body, may be externally applied to the nanogenerator 100. In sucha case, the at least one nanostructure 140 on the substrate 110 may bedeformed. Referring to FIG. 1B, a portion 141 of at least onenanostructure 140 may bend flexibly, and another portion 143 maycontract in a lengthwise direction when the mechanical force is appliedto the at least one nanostructure 140. When the application of themechanical force ends, the at least one nanostructure 140 returns backto the original state. Since the at least one nanostructure 140 haspiezoelectric characteristics, the at least one nanostructure 140 mayinduce a voltage between the first and second electrodes 130 and 120connected to both ends of the at least one nanostructure 140. Thus, thenanogenerator 100 may convert mechanical energy into electric energy.

The nanogenerator 100 includes the at least one nanostructure 140 withorganic piezoelectric material having good piezoelectriccharacteristics, and may thus effectively convert mechanical energygenerated from, for example, fine vibrations or motion to electricenergy. The at least one nanostructure 140 including PVDF has betterpiezoelectric characteristics than a ZnO nanostructure. In addition, apiezoelectric material, such as lead zirconate titanate (PZT), containslead (Pb), and is therefore harmful to human bodies. Also, forming ananostructure using PZT is difficult. On the other hand, since the atleast one nanostructure 140 including PVDF is chemically stable, and isnot harmful to human bodies, it may thus be applied to human bodies.Also, the at least one nanostructure 140 including PVDF is flexible andmay therefore be used to manufacture a flexible nano device. When nanodevices are driven by using the nanogenerator 100, the sizes of the nanodevices may be minimized and the performances of the nano devices may beenhanced. Furthermore, the nano devices may be independently driven.

FIG. 2A is a schematic perspective view of a nanogenerator 200 accordingto another embodiment. FIG. 2B is a schematic top plan view of thenanogenerator 200 of FIG. 2A.

Referring to FIGS. 2A and 2B, the nanogenerator 200 may include asubstrate 210, a plurality of electrodes 221, 223, 225, and 227 disposedapart from one another on the substrate 210, and at least onenanostructure 240 disposed between the plurality of electrodes 221, 223,225, and 227.

Any of various types of substrates may be used as the substrate 210. Forexample, the substrate 210 may be a solid substrate, such as a glasssubstrate or a silicon substrate, or a flexible substrate, such as aplastic substrate or a textile substrate, but aspects of the presentinvention are not limited thereto.

The plurality of electrodes 221, 223, 225, and 227 may be disposed apartfrom one another on the substrate 210. The plurality of electrodes 221,223, 225, and 227 may be disposed in parallel on the substrate 210 atpredetermined intervals. Each of the plurality of electrodes 221, 223,225, and 227 may be formed of a material selected from the groupconsisting of gold (Au), silver (Ag), aluminum (Al), copper (Cu),palladium (Pd), platinum (Pt), ruthenium (Ru), and mixtures thereof. Inother embodiments, each of plurality of electrodes 221, 223, 225, and227 may be formed of an indium tin oxide (ITO), a carbon nanotube, aconductive polymer, nanofiber, a nanocomposite, or graphene. However,the materials of the electrodes are not limited thereto. The at leastone nanostructure 240 may be disposed between the plurality ofelectrodes 221, 223, 225, and 227. The at least one nanostructure 240may be disposed perpendicularly or inclined at a predetermined anglewith respect to the plurality of electrodes 221, 223, 225, and 227.Also, the at least one nanostructure 240 may be respectively disposedinclined at a random angle with respect to the plurality of electrodes221, 223, 225, and 227. The plurality of electrodes 221, 223, 225, and227 may be connected in series via the at least one nanostructure 240disposed between the plurality of electrodes 221, 223, 225, and 227. Ahigher voltage may be obtained when the plurality of electrodes 221,223, 225, and 227 are connected in series than when the plurality ofelectrodes 221, 223, 225, and 227 are not connected in series.

An external load 250 may be connected to the outermost electrodes 221and 227 from among the plurality of electrodes 221, 223, 225, and 227 soas to store or consume electricity generated by the nanogenerator 200.FIGS. 2A and 2B illustrate a case where four electrodes 221, 223, 225,and 227 are disposed on the substrate 210, but embodiments are notlimited thereto and at least two electrodes may be disposed on thesubstrate 210.

The at least one nanostructure 240 may include an organic piezoelectricmaterial, e.g., a ferroelectric material. For example, the at least onenanostructure 240 may include polyvinylidene fluoride (PVDF). Morespecifically, the at least one nanostructure 240 may include β-phasePVDF. If the at least one nanostructure 240 includes PVDF, the at leastone nanostructure 240 may be formed using an anodic aluminum oxidetemplate. The at least one nanostructure 240 may include a nanorod, ananowire, or a nanotube. The nanorod and the nanowire may have differentaspect ratios. For example, the aspect ratio of the nanowire may begreater or less than that of the nanorod. The size and cross-sectionalshape of the at least one nanostructure 240 may vary according to thoseof the anodic aluminum oxide template.

A mechanical force, e.g., fine vibrations, wind, sound, or the motion ofa human body, may be externally applied to the nanogenerator 200. Insuch a case, the at least one nanostructure 240 on the substrate 210 maybe deformed. Referring to FIG. 2B, a portion 243 of the at least onenanostructure 240 may bend flexibly, and another portion 241 maycontract in a lengthwise direction when the mechanical force is appliedto the at least one nanostructure 240. When the application of themechanical force ends, the at least one nanostructure 240 returns backto the original state. Since the at least one nanostructure 240 has suchpiezoelectric characteristics, the at least one nanostructure 240 mayinduce a voltage between the plurality of electrodes 221, 223, 225, and227 connected to the at least one nanostructure 240. Thus, thenanogenerator 200 may convert mechanical energy into electric energy.Although FIG. 2B illustrates a case where an external force is appliedin a direction parallel to the substrate 210, embodiments are notlimited thereto and the external force may be applied in a directionother than parallel to the substrate, e.g., perpendicular to thesubstrate 210. In this case, the at least one nanostructure 240 mayflexible bend in the direction perpendicularly to the substrate 210.

In the nanogenerator 200, a low voltage may be generated betweenadjacent every two electrodes from among the plurality of electrodes221, 223, 225, and 227. However, since all of the plurality ofelectrodes 221, 223, 225, and 227 are connected in series, a highervoltage may be obtained in the nanogenerator 200 by increasing the totalnumber of electrodes therein.

The nanogenerator 200 includes the at least one nanostructure 240 withorganic piezoelectric material having good piezoelectriccharacteristics, and may thus effectively convert mechanical energygenerated from, for example, fine vibrations or motion to electricenergy. The at least one nanostructure 240 including PVDF has betterpiezoelectric characteristics than a ZnO nanostructure. A piezoelectricmaterial, such as lead zirconate titanate (PZT), contains lead (Pb), andis therefore harmful to human bodies. Also, forming a nanostructure byusing PZT is difficult. On the other hand, since the at least onenanostructure 240 including PVDF is chemically stable, and is notharmful to human bodies, it may therefore be applied to human bodies.Also, the at least one nanostructure 240 including PVDF is flexible andmay therefore be used to manufacture a flexible nano device. When nanodevices are driven by using the nanogenerator 200, the sizes of the nanodevices may be minimized and the performances of the nano devices may beenhanced. Furthermore, the nano devices may be independently driven.

Methods of manufacturing a nanogenerator according to exemplaryembodiments are described below.

FIGS. 3A to 3C are schematic cross-sectional views sequentiallyillustrating a method of manufacturing the nanogenerator 100 illustratedin FIGS. 1A and 1B, according to an embodiment. Referring to FIG. 3A,the substrate 110 may be prepared, and the second electrode 120 may beformed on the substrate 110. Any of the previously mentioned varioustypes of substrates may be used as the substrate 110. For example, thesubstrate 110 may be a solid substrate, such as a glass substrate or asilicon substrate, or a flexible substrate, such as a plastic substrateor a textile substrate, but the materials of the substrate are notlimited thereto.

The second electrode 120 may be formed of a material selected from thegroup consisting of gold (Au), silver (Ag), aluminum (Al), copper (Cu),palladium (Pd), platinum (Pt), ruthenium (Ru), and mixtures thereof. Inother embodiments, each of the first electrode 130 and the secondelectrode 120 may be formed of an indium tin oxide (ITO), a carbonnanotube, a conductive polymer, nanofiber, a nanocomposite, or graphene.However, the materials of the electrodes are not limited thereto. Whenthe substrate 110 contains a conductive material, the substrate 110 maybe used as an electrode instead of the second electrode 120, and thesecond electrode 120 may thus not be formed on the substrate 110.

Referring to FIG. 3B, at least one nanostructure 140 may be formed onthe second electrode 120. The at least one nanostructure 140 may beformed on the second electrode 120 in an m×n 2D array. Here, m and neach denote a natural number. In other words, one nanostructure 140 maybe formed on the second electrode 120 or a plurality of nanostructures140 may be formed in parallel on the second electrode 120 to be apartfrom one another by a predetermined distance. Also, the at least onenanostructure 140 may be disposed perpendicularly or inclined at apredetermined angle with respect to the substrate 110.

The at least one nanostructure 140 may include an organic piezoelectricmaterial, e.g., a ferroelectric material. For example, the at least onenanostructure 140 may include polyvinylidene fluoride (PVDF). In such acase, the at least one nanostructure 140 may be formed using an anodicaluminum oxide template. The at least one nanostructure 140 may includea nanorod, a nanowire, or a nanotube. The nanorod and the nanowire mayhave different aspect ratios. For example, the aspect ratio of thenanowire may be greater or less than that of the nanorod. The size andsectional shape of the at least one nanostructure 140 may vary accordingto those of the anodic aluminum oxide template. A method of forming theat least one nanostructure 140 will be described in detail withreference to FIGS. 4A to 4D or FIGS. 5A to 5E below.

Referring to FIG. 3C, the first electrode 130 may be formed on the atleast one nanostructure 140. The first electrode 130 may be disposedapart from the substrate 110 by a predetermined distance. The firstelectrode 130 may be formed of a material selected from the groupconsisting of gold (Au), silver (Ag), aluminum (Al), copper (Cu),palladium (Pd), platinum (Pt), ruthenium (Ru), and mixtures thereof. Inother embodiments, the first electrode 130 may be formed of an indiumtin oxide (ITO), a carbon nanotube, a conductive polymer, nanofiber, ananocomposite, or graphene. However, the materials of the electrodes arenot limited thereto. A stack structure of the at least one nanostructure140 and a third electrode 131 of FIG. 7 on the at least onenanostructure 140 may further be formed at least once on the firstelectrode 130. For example, referring to FIG. 7, the third electrode 131is further formed to be apart from the first electrode 130 by apredetermined distance, and the at least one nanostructure 140 mayfurther be formed between the first and third electrodes 130 and 131.Then, a fourth electrode 132 may further be formed to be apart from thethird electrode 131 by a predetermined distance, and the at least onenanostructure 140 may further be formed between the third and fourthelectrodes 131 and 132.

FIGS. 4A to 4D are schematic cross-sectional views sequentiallyillustrating a method of manufacturing the at least one nanostructure140 of FIGS. 1A and 1B, according to an embodiment. Referring to FIG.4A, first, an anodic metal oxide template 310 may be prepared. Theanodic metal oxide template 310 may include a metal layer 311 and aporous layer 313 on the metal layer 311. The anodic metal oxide template310 may be, for example, an anodic aluminum oxide (AAO) template. As anexample, the anodic aluminum oxide template may be obtained byperforming at least one anodic oxidation process on aluminum foil. Inthe anodic oxidation process, the aluminum foil may be dipped into anoxalic acid solution or a sulfuric acid solution at about 15° C. and avoltage of about 40V may be applied thereto to obtain a porous anodicaluminum oxide template. Then, the porous anodic aluminum oxide templatemay be etched using a phosphoric acid solution to adjust the size anddepth of each hole therein. As an example, if the porous anodic aluminumoxide template is formed having deep holes, by increasing the etch time,then the porous anodic aluminum oxide template may provide for ananowire rather than a nanorod.

Referring to FIG. 4B, a solution 145 containing an organic piezoelectricmaterial may be filled into the anodic metal oxide template 310. Theorganic piezoelectric material may be a ferroelectric material, e.g.,PVDF. More specifically, the organic piezoelectric material may includeβ-phase PVDF. The solution 145 may be obtained by dissolving the organicpiezoelectric material using a solvent, such as butanol ordimethylformamide (DMF) or another solvent suitable for dissolving theorganic piezoelectric material. The solution 145 may be filled intoholes formed in the porous layer 313 in any suitable manner. Forexample, in order to fill the porous layer 313 with the solution 145,the solution 145 may be sprayed onto the porous layer 313 or the anodicmetal oxide template 310 may be dipped into the solution 145. The porouslayer 313 may be easily filled with the solution 145 when thetemperature of the solution is at about 50 to about 250. For example,the porous layer 313 may be filled with the solution 145 containing theorganic piezoelectric material when the temperature of the solution isat about 150. In other embodiments, the porous layer 313 may be filledwith the solution 145 in a vacuum. Nanowires (nanorods) or nanotubeswith the organic piezoelectric material may be formed by adjusting theweight percentage (wt %) of the organic piezoelectric material in thesolution 145. For example, if the weight percentage (wt %) of theorganic piezoelectric material is high, it is possible to form nanowires(nanorods) using the organic piezoelectric material. In otherembodiments, it is possible to form nanowires (nanorods) with theorganic piezoelectric material by repeatedly filling the solution 145 inthe porous layer 313.

Referring to FIG. 4C, poling, that is, recrystallization, may beperformed on the organic piezoelectric material filled in the porouslayer 313 to form the nanostructure 140. The organic piezoelectricmaterial may be poled when the temperature of the organic piezoelectricmaterial is at about 50° C. to about 250° C. For example, the organicpiezoelectric material may be poled when the temperature of the organicpiezoelectric material is at about 150° C. In some embodiments, a thinfilm formed on the porous layer 313 with the solution 145 containing theorganic piezoelectric material may be removed. The thin film may beremoved, for example, by performing an oxygen plasma process.

Referring to FIG. 4D, the porous layer 313 may be removed. The manner ofremoving porous layer 313 is not particularly limited. The porous layer313 may be removed, for example, by a wet etching process using a NaOHsolution. Using such a process, the at least one nanostructure 140 maybe formed on the metal layer 311. In some embodiments, the metal layer311 may be used as the second electrode 120 included in thenanogenerator 100 of FIGS. 1A and 1B. Alternatively, the metal layer 311may be removed together with the porous layer 313. Similarly, thenanostructure 240 illustrated in FIGS. 2A and 2B may be formed.

FIGS. 5A to 5E are schematic cross-sectional views sequentiallyillustrating a method of manufacturing the at least one nanostructure140 included in the nanogenerator 100 of FIGS. 1A and 1B, according toanother embodiment. Referring to FIG. 5A, first, the anodic metal oxidetemplate 310 may be prepared. The anodic metal oxide template 310 mayinclude a metal layer 311 and a porous layer 313 on the metal layer 311.The anodic metal oxide template 310 may be, for example, an anodicaluminum oxide (AAO) template. In one embodiment, the anodic aluminumoxide template may be obtained by performing at least one anodicoxidation process on aluminum foil. In the anodic oxidation process, thealuminum foil may be dipped into an oxalic acid solution or a sulfuricacid solution at about 15° C. and a voltage of about 40V may be appliedthereto to obtain a porous anodic aluminum oxide template. Then, theporous anodic aluminum oxide template may be etched using, for example,a phosphoric acid solution to adjust the size and depth of each holetherein.

Referring to FIG. 5B, the metal layer 311 may be removed from the anodicmetal oxide template 310 so that only the porous layer 313 may remain inthe anodic metal oxide template 310. The manner of removing the metallayer 311 is not particularly limited. For example, the metal layer 311may be removed by a wet etching process using, for example, a NaOHsolution.

Referring to FIG. 5C, a solution 145 containing an organic piezoelectricmaterial may be filled in the remaining porous layer 313 using anysuitable method. The organic piezoelectric material may be aferroelectric material, e.g., PVDF. More specifically, the organicpiezoelectric material may include β-phase PVDF. The solution 145 may beobtained by dissolving the organic piezoelectric material in anysuitable solvent, e.g., butanol or dimethylformamide (DMF). The solution145 may be filled in holes formed in the porous layer 313 in anysuitable manner. For example, order to fill the porous layer 313 withthe solution 145, the solution 145 may be sprayed onto the porous layer313 or the anodic metal oxide template 310 may be dipped into thesolution 145. Since the holes in the porous layer 311 are through holes,that is, both ends of the holes of the porous layer 311 are open, thesolution 145 may be easily and rapidly entered into the holes. Theporous layer 313 may be easily filled with the solution when thetemperature of the solution is 145 at about 50° C. to about 250° C. Forexample, the porous layer 313 may be filled with the solution 145containing the organic piezoelectric material when the temperature ofthe solution is at about 150° C. In another embodiment, the porous layer313 may be filled with the solution 145 in a vacuum. It is possible toform nanowires (or nanorods) or nanotubes with the organic piezoelectricmaterial by adjusting the weight percentage (wt %) of the organicpiezoelectric material in the solution 145. For example, if the weightpercentage (wt %) of the organic piezoelectric material is low, it ispossible to form nanotubes by using the organic piezoelectric material.

Referring to FIG. 5D, poling may be performed on the organicpiezoelectric material filled in the porous layer 313 to form thenanostructure 140. The organic piezoelectric material may be poled whenthe temperature of the organic piezoelectric material is at about 50° C.to about 250° C. For example, the organic piezoelectric material may bepoled when the temperature of the organic piezoelectric material is atabout 150° C. In some embodiments, a thin film formed on the porouslayer 313 with the solution 145 containing the organic piezoelectricmaterial may be removed. The thin film may be removed, for example, byperforming an oxygen plasma process.

Referring to FIG. 5E, the porous layer 313 may be removed by anysuitable manner. The porous layer 313 may be removed by a wet etchingprocess, for example, using a NaOH solution, thereby forming the atleast one nanostructure 140. Similarly, the nanostructure 240illustrated in FIGS. 2A and 2B may be formed.

FIGS. 6A and 6B are schematic cross-sectional views sequentiallyillustrating a method of manufacturing the nanogenerator 200 of FIGS. 2Aand 2B, according to another embodiment. Referring to FIG. 6A, theplurality of electrodes 221, 223, 225, and 227 may be formed on thesubstrate 210. Any of the previously disclosed various types ofsubstrates may be used as the substrate 210. For example, the substrate210 may be a solid substrate, such as a glass substrate or a siliconsubstrate, or a flexible substrate, such as a plastic substrate or atextile substrate, but aspects of the present invention are not limitedthereto.

The plurality of electrodes 221, 223, 225, and 227 may be disposed inparallel on the substrate 210 at predetermined intervals. Each of theplurality of electrodes 221, 223, 225, and 227 may be formed of amaterial selected from the group consisting of gold (Au), silver (Ag),aluminum (Al), copper (Cu), palladium (Pd), platinum (Pt), ruthenium(Ru), and mixtures thereof. In other embodiments, each of plurality ofelectrodes 221, 223, 225, and 227 may be formed of an indium tin oxide(ITO), a carbon nanotube, a conductive polymer, nanofiber, ananocomposite, or graphene. However, the materials of the electrodes arenot limited thereto.

Referring to FIG. 6B, the at least one nanostructure 240 may be disposedbetween the plurality of electrodes 221, 223, 225, and 227. The at leastone nanostructure 240 may be disposed perpendicularly or inclined at apredetermined angle with respect to the plurality of electrodes 221,223, 225, and 227. Also, the at least one nanostructure 240 may berespectively disposed inclined at a random angle with respect to theplurality of electrodes 221, 223, 225, and 227.

The at least one nanostructure 240 may include an organic piezoelectricmaterial, e.g., a ferroelectric material. For example, the at least onenanostructure 240 may include polyvinylidene fluoride (PVDF). Morespecifically, the at least one nanostructure 140 may include β-phasePVDF. If the at least one nanostructure 240 includes PVDF, the at leastone nanostructure 240 may be formed using an anodic aluminum oxidetemplate. The at least one nanostructure 240 may include a nanorod, ananowire, or a nanotube. The nanorod and the nanowire may have differentaspect ratios. For example, the aspect ratio of the nanowire may begreater than or less than that of the nanorod. The size and sectionalshape of the at least one nanostructure 240 may vary according to thoseof the anodic aluminum oxide template. A method of forming the at leastone nanostructure 240 is as described above with reference to FIGS. 4Ato 4D or FIGS. 5A to 5E.

FIG. 7 is a schematic cross-sectional view of a nanogenerator 300according to another embodiment. Referring to FIG. 7, the nanogenerator300 may include a substrate 110, a first electrode 130 disposed apartfrom the substrate 110 by a predetermined distance, and at least onenanostructure 140 disposed between the substrate 110 and the firstelectrode 130. In the nanogenerator 300, a stack structure of the atleast one nanostructure 140 and a third electrode 131 on the at leastone nanostructure 140 may be formed at least once on the first electrode130. The nanogenerator 300 may further include a second electrode 120 onthe substrate 110. The at least one nanostructure 140 may be disposedbetween the first and second electrodes 130 and 120 and between thefirst and third electrodes 130 and 131.

Any of the previously disclosed various types of substrates may be usedas the substrate 110. For example, the substrate 110 may be a solidsubstrate, such as a glass substrate or a silicon substrate, or aflexible substrate, such as a plastic substrate or a textile substrate,but aspects of the present invention are not limited thereto.

The first electrode 130 may be disposed apart from the substrate 110 bythe predetermined distance, and the second electrode 120 may be furtherdisposed on the substrate 110. Each of the first electrode 130 and thesecond electrode 120 may be formed of a material selected from the groupconsisting of gold (Au), silver (Ag), aluminum (Al), copper (Cu),palladium (Pd), platinum (Pt), ruthenium (Ru), and mixtures thereof. Inother embodiments, each of the first electrode 130 and the secondelectrode 120 may be formed of an indium tin oxide (ITO), a carbonnanotube, a conductive polymer, nanofiber, a nanocomposite, or graphene.However, the materials of the electrodes are not limited thereto. Whenthe substrate 110 contains a conductive material, the substrate 110 maybe used as an electrode instead of the second electrode 120. Forexample, if the substrate 110 contains high-concentration doped silicon,the second electrode 120 may not be formed on the substrate 110.

The at least one nanostructure 140 may be disposed between the firstelectrode 130 and the second electrode 120. The at least onenanostructure 140 may be formed on the second electrode 120 in an m×n 2Darray. Here, m and n each denote a natural number. In other words, onenanostructure 140 may be disposed on the second electrode 120 or aplurality of nanostructures 140 may be disposed in parallel on thesecond electrode 120 to be apart from one another by a predetermineddistance. Also, the at least one nanostructure 140 may be disposedperpendicularly or inclined at a predetermined angle with respect to thesubstrate 110.

A stack structure of the at least one nanostructure 140 and the thirdelectrode 131 on the at least one nanostructure 140 may be formed atleast once on first electrode 130. For example, referring to FIG. 7, thethird electrode 131 may be disposed apart from the first electrode 130by a predetermined distance, and the a fourth electrode 132 may bedisposed apart from the third electrode 131 by a predetermined distance.In other words, the first to fourth electrodes 130, 120, 131, and 132may be disposed to be parallel with one another, but the presentembodiments are not limited thereto. The at least one nanostructure 140may be also disposed between the first and third electrodes 130 and 131and between the third and fourth electrodes 131 and 132. Each of thethird and fourth electrodes 131 and 132 may be formed of a materialselected from the group consisting of gold (Au), silver (Ag), aluminum(Al), copper (Cu), palladium (Pd), platinum (Pt), ruthenium (Ru), andmixtures thereof. In other embodiments, each of the third and fourthelectrodes 131 and 132 may be formed of an indium tin oxide (ITO), acarbon nanotube, a conductive polymer, nanofiber, a nanocomposite, orgraphene. However, the materials of the electrodes are not limitedthereto.

The at least one nanostructure 140 may include an organic piezoelectricmaterial, e.g., a ferroelectric material. For example, the at least onenanostructure 240 may include polyvinylidene fluoride (PVDF). Morespecifically, the at least one nanostructure 140 may include β-phasePVDF. If the at least one nanostructure 140 includes PVDF, the at leastone nanostructure 140 may be formed using an anodic aluminum oxidetemplate. The at least one nanostructure 140 may include a nanorod, ananowire, or a nanotube. The nanorod and the nanowire may have differentaspect ratios. For example, the aspect ratio of the nanowire may begreater than or less than that of the nanorod. The size and sectionalshape of the at least one nanostructure 140 may vary according to thoseof the anodic aluminum oxide template.

An external load 150 may be connected to the outermost electrodes 120and 132 from among the first to fourth electrodes 130, 120, 131, and 132so as to store or consume electricity generated by the nanogenerator300. For example, if the external load 150 is a capacitor, theelectricity generated by the nanogenerator 300 may be stored in thecapacitor. If the external load 150 is a nano device, the electricitygenerated by the nanogenerator 300 may be consumed by the nano device.

A mechanical force, e.g., fine vibrations, wind, sound, or the motion ofa human body, may be externally applied to the nanogenerator 300. Insuch a case, the at least one nanostructure 140 on the substrate 110 maybe deformed. Referring to FIG. 7, a portion 141 of the at least onenanostructure 140 may bend flexibly, and another portion 143 maycontract in a lengthwise direction when the mechanical force is appliedto the at least one nanostructure 140. When the application of themechanical force ends, the at least one nanostructure 140 returns backto the original state. Since the at least one nanostructure 140 haspiezoelectric characteristics, the at least one nanostructure 140 mayinduce a voltage between the first and second electrodes 130 and 120,between the first and third electrodes 130 and 131 and between the thirdand fourth electrodes 131 and 132 from among the first to fourthelectrodes 130, 120, 131, and 132 connected to both ends of the at leastone nanostructure 140. The first to fourth electrodes 130, 120, 131, and132 may be connected in series via the at least one nanostructure 140disposed therebetween. A higher voltage may be generated in thenanogenerator 300 when the first to fourth electrodes 130, 120, 131, and132 are connected in series than when the first to fourth electrodes130, 120, 131, and 132 are not connected in series.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

What is claimed is:
 1. A nanogenerator comprising a plurality ofnanostructures comprising an organic piezoelectric material and disposedapart from each other, a first electrode, a second electrode, and asubstrate, wherein the first electrode and second electrode are disposedapart from each other, wherein each of the plurality of nanostructuresis interposed between the first electrode and the second electrode, andwherein the first electrode and the second electrode are directly formedon the substrate.
 2. The nanogenerator of claim 1, wherein the organicpiezoelectric material is a ferroelectric material.
 3. The nanogeneratorof claim 2, wherein the organic piezoelectric material is polyvinylidenefluoride.
 4. The nanogenerator of claim 1, wherein the substratecomprises a conductive material.
 5. The nanogenerator of claim 1,wherein at least one of the plurality of nanostructures is disposedperpendicularly or inclined at a predetermined angle with respect to thefirst electrode.
 6. The nanogenerator of claim 1, further comprising athird electrode disposed apart from the first electrode, wherein theplurality of nanostructures comprise at least a first nanostructureinterposed between the first electrode and the second electrode, and asecond nanostructure interposed between the first electrode and thethird electrode.
 7. The nanogenerator of claim 1, further comprising aplurality of electrodes disposed apart from one another, wherein each ofthe plurality of nanostructures is interposed between the plurality ofelectrodes.
 8. The nanogenerator of claim 7, wherein the plurality ofelectrodes and the plurality of nanostructures are disposed on thesubstrate.
 9. The nanogenerator of claim 7, wherein the plurality ofelectrodes are disposed in parallel at predetermined intervals.
 10. Thenanogenerator of claim 7, wherein at least one of the plurality ofnanostructures is disposed perpendicularly or inclined at apredetermined angle with respect to the plurality of electrodes.
 11. Thenanogenerator of claim 7, wherein the plurality of electrodes areconnected in series.
 12. A method of generating energy comprisingapplying an external force to the nanogenerator of claim
 1. 13. Themethod of generating energy of claim 12 in which the plurality ofnanostructures comprise polyvinylidene fluoride.
 14. A method of storingenergy comprising: generating energy from the nanogenerator of claim 1,and storing the energy in a capacitor connected to the nanogenerator.15. The method of storing energy of claim 14, wherein the nanogeneratorcomprises polyvinylidene fluoride.